This invention relates to aircraft landing gear.
With modern passenger-carrying aircraft becoming ever larger and more complex the retraction and stowage of landing gear, especially wing and body main landing gear, is becoming ever more difficult. Sometimes retraction action of the gear can be restricted by the proximity of other gears or equipment or by a restricted entry into the stowage bay and the avoidance of such problems can create considerable difficulties for the designer, potentially resulting in completely redesigning the landing gear configuration for the aircraft, or if not then often the addition of substantial extra weight by the use of a non optimum design to avoid the retraction problem.
An object of the present invention is to provide a landing gear in which such problems will be removed or at least alleviated.
According to a first aspect of the invention there is provided an aircraft landing gear comprising a wheeled leg and a plurality of leg mounting members to be attached to an airframe of the aircraft via respective attachments, the leg being pivotably movable between a first stowed position within the aircraft and a second deployed position for movement of the aircraft along the ground, at least one of the attachments being configured to allow retraction movement of the leg to occur about an angularly variable pivot axis.
In this way, whilst pivotal retraction (or deployment) movement takes place, parts of the gear liable to contact other parts of the aircraft may be caused to move clear of the obstacle by varying the pivot axis during the pivotal movement.
It is envisaged that the angular variation of the pivot axis may be achieved in any convenient way, for example by providing the at least one attachment with at least one cam track to guide the said pivotal movement, or by forming the at least one attachment with a pair of links, or by forming the at least one attachment by a series of variable length links such as sprung links or hydraulic actuators. It is envisaged that any number of ways could be used to achieve the pivotal movement of the gear about a variable pivot axis and this invention is intended to cover any such way.
In the attachment with the pair of links, the links are preferably arranged to allow a small amount of free movement in a given direction when the gear is in the deployed position but to restrict movement in other directions and preferably to allow only controlled pivotal retraction movement of the gear. In this way, if the gear employs four point location in the deployed position, using two side stays in conjunction with fore and aft pintle mountings for example, then a slight amount of free up and down movement in the deployed position may be allowed by the links. This may be achieved by arranging at least one of the links, and possibly both links, substantially horizontally in the deployed position. This freedom to move afforded by the invention, in the deployed position, will then alleviate unwanted stresses caused by the statically indeterminate structure created by the four point location when gear deflection occurs during taxing or takeoff or landing, or with wing deflection in flight before the gear is retracted.
The controlled pivotal retraction movement may be achieved by arranging for the links to be substantially in plane, in the deployed position, and substantially out of plane as soon as retraction movement commences. This may therefore be achieved by having spaced pivot axes for the links and preferably by having links of unequal length. Most preferably in one embodiment, links of unequal length having spaced pivot axes are arranged for a forward pintle mounting for the gear with the links being substantially in plane and horizontal in the gear deployed position. Thus, with two side stays and a rear pintle mounting in conjunction with the forward pintle mounting, a small amount of up and down movement of the forward pintle mounting part of the gear will be allowed when deployed but torque induced in a main leg of the gear, for example during turning, will be reacted by the attachment of the invention.
In another embodiment the invention may include a resilient element interposed between a pivotal attachment to the aircraft structure of a said link and the leg, effectively to allow limited length changes in the said link upon deflections of the aircraft structure.
The resilient element may comprise a torque shaft connecting a crank on the leg, to which the said link is pivotably attached, to the leg.
The torque shaft conveniently extends within a passage defined in the leg.
According to a second aspect of the invention there is provided an aircraft wing having landing gear thereon according to the first aspect of the invention.
According to a third aspect of the invention there is provided an aircraft fuselage including landing gear according to the first aspect of the invention.
According to a fourth aspect of the invention there is provided an aircraft having a landing gear according to the first said aspect of the invention.